Working with volatile liquids and gases is an everyday occurrence in pharmaceutical and chemical industries, often involving hazardous such as explosive, atmospheres (ATEX rated 1/21). This has meant that use of control cabinets combining electrical and pneumatic devices has been deemed highly dangerous due to the risk of corrosion of electrical parts, which could subsequently cause an explosion. A new solution is claimed to permit the combination of electrical and pneumatic devices with Fieldbus communications, even in zone 1/21 environments. Developed by Burkert, this combines the company’s AirLINE Ex 8650 system with modules from the intrinsically safe SIMATIC ET 200iSP system from Siemens. It provides users with a complete ATEX certified unit for use in zone 1/21, achieving cost savings by delivering substantial reductions in cabinet space, wiring, documentation and validation.
Until recently, combining electrical and pneumatic devices in control cabinets in zone 1/21 environments could prove impossible due to the wet and oily compressed air, which caused corrosion and short circuits. Today, however, compressed air systems usually work with air qualities with a pressure dew point below -20degC (residual moisture of 0,88 g/m³) and an oil concentration of less than 1 mg/m³. Moreover, Burkert reports that, in the pharmaceutical and food & beverage sectors, even better compressed air quality can be expected; by several orders of magnitude. According to Burkert, the quality of the exhausted compressed air is so good that it can be channelled into the control cabinet in order to prevent humidity or dust within the ambient air from entering the cabinet. With this arrangement a pressure release facility or exhauster is, of course, necessary.

Reduced wiring effort
Whilst working with dry and oil-free air reduces the problem of corrosion and short circuits, there is still a detonation risk that remains due to the process conditions. In zone 1/21 hazardous areas, the pneumatic control of cylinders and pneumatic actuators is generally achieved with either discrete explosion-proof valves, directly mounted to the actuator, or Ex-proof valve banks wired to a remote-I/O-system. Installing the pilot valves in a safe area is a further option – although often not possible as the large distances between valves and actuators lead to unacceptably long switching times. However, Burkert comments that connecting sensors and actuators to bus systems substantially reduces the wiring effort.
The use of advanced Profibus DPV1 communications relieves the control engineer of the task of installing the many special expensive electrical junctions and terminations required by conventional field wired systems in ATEX areas. It can also offer additional major benefits, including a more compact control system, a more ‘close-to-the-process’ installation, simplified documentation, minimal power consumption, and, hence, significant cost savings. In addition, the new ex-proof electro-pneumatic automation system is claimed to offer another advantage: all elements, valves (etc) are harmonised and certified. This means that users do not have to provide evidence of the safety of the system. Instead, Burkert provides a certificate covering the complete control cabinet, enabling users to guarantee that all devices and elements are consistent to EN 60079 part 0/1/7/11/26 and EN 60529. As Burkert’s AirLINE Ex 8650 unit is fully certified, it can be used in explosion-hazard areas with gas or dust atmospheres. The system is particularly suited to decentralised process control tasks concerning fine chemicals, pharmaceuticals and cosmetics; and it can be employed anywhere where solvents, alcohol or lacquers are utilised. It can even be installed for direct factory automation; for example. for the automatic filling of solvents, alcohol or lacquers.

Fast and easy system set-up
Burkert maintains that standardised interfaces and a flexible and modular design guarantee a fast and easy system set-up and allow pneumatic, electric and electronic modules with diverse functions to be combined with each other. The system allows up to 48 Burkert EExia solenoid valves to be seamlessly combined with Siemens ET200iSP EExia/ib electronic digital and analogue I/O modules in single distributed I/O assemblies.